1. Field of the Invention
The present invention relates to a combustion head, in particular for gas burners of the type involving the use of an internally hollow mixing body and means for feeding a combustible gas-combustion air mixture into the mixing body, said combustion head being provided with delivery ports through which the combustible gas-combustion air mixture is ejected from the mixing body and fired.
In the above described solution the combustion head in question is conceived in particular for employment in small boilers and similar heating apparatuses for home use. However, the innovatory concepts suggested by the present invention can be validly adopted to produce any other type of burner, be it an atmospheric or an aerated burner with forced ventilation, to be also employed in furnaces or heating systems of an industrial type.
2. Prior Art
It is known that burners normally used in boilers, furnaces or other heating systems for domestic and/or industrial use fed with gaseous fuel essentially consist of an internally hollow mixing body generally of a box-shaped structure, provided with means for the controlled admission of a combustible gas and combustion air drawn from the surrounding atmosphere. Associated with the upper part of the mixing body is a combustion head in which a plurality of ports is formed for delivery of the combustible gas-combustion air mixture from the inside of the mixing body.
In burners of the most widely spread type, said delivery ports essentially consist of mere through holes having a round or shaped configuration, formed through a metal plate constituting the combustion head. The combustible gas-combustion air mixture is fired at the exit of said through holes, thereby forming a plurality of flames arising from the external surface of the combustion head. While the combustion heads of the above type are adopted in many situations, they however have some drawbacks in terms of burning efficiency. In particular, the air-gas mixing carried out within the mixing body does not always appear sufficiently efficient to ensure an optimal and intimate mingling of the two components, which is essential for achieving a correct burning.
There are also burners the combustion head of which essentially consists of a wire net having meshes of an appropriate size to give the outgoing gas-air mixture such a speed that the risk of backfire towards the mixing body is avoided. In burners of this type, burning gives rise to a continuous flame front substantially covering the whole external surface of the combustion head. In addition, heat resulting from combustion taking place in direct contact with the wire net causes said net to become incandescent and, as a result, to dissipate heat by radiation. Hence it follows that the combustion heads of this type ensure a combustion of better quality as compared with those described beforehand, but on the other hand they have a drawback too in that the wire nets, in addition to being very expensive, exhibit a structural brittleness that in many cases makes it inconvenient to use them.
Also provided are other burners the combustion head of which substantially consists of one or more plates made of a ceramic material having a honeycomb structure and obtained by molding. These ceramic plates have a greater structural strength than the previously described wire nets, but they involve high production costs too and, in addition, have a reduced resistance to thermal shocks. Furthermore, also in burners provided with such a type of combustion head, the gas-air mixing carried out within the mixing body does not prove to be sufficient for ensuring an optimal combustion development, above all in the cases in which the air and gas flow rate values must be adjusted for achieving a flame modulation.
Burners have been also manufactured in which the combustion head essentially consists of a porous ceramic material or a non-woven fabric formed of ceramic material fibers. This type of combustion head has a greater resistance to thermal shocks as compared with that of the ceramic material plates. However, also porous ceramic materials and non-woven fabrics involve high production costs and above all do not allow a precise measurement of the delivery ports embodied by the hollow spaces created between the various ceramic material fibers or particles having a random orientation. Therefore very thick porous materials or non-woven fabrics need to be adopted. But, on the other hand, an important thickness appears to be inappropriate, due to the flow resistance induced on the outgoing mixture, for use on burners of the atmospheric type requiring air to be fed by forced ventilation. An important thickness also involves the installation of auxiliary air and/or gas filtering devices, in order to avoid the risk that dust or other impurities may obstruct the hollow spaces between the ceramic fibers or particles, impairing the thereby burner operation.